1. Field of the Invention
The invention relates to a device for holding the ends of the turns of a stator winding in a dynamo-electric machine, comprising a rotor and a stator and a stator housing, which stator has a laminated core with stator core end plates at the end, there being arranged in slots in the laminated core a stator winding which has bottom and top bars and the ends of which overlap the laminated core axially, which holder has an inner ring which fits closely, either directly or with the interposition of all interlayer, against the ends of the turns of the stator winding, which ends widen like an internal taper, and which has a multipart external support comprising rings and supporting brackets, which supporting brackets are attached to the end of the laminated core.
In this regard, the invention refers to a prior art as disclosed, for example, in U.S. Pat. No. 5,140,740, identical in content to the latter.
2. Discussion of Background
Fastening the ends of the windings of the stator windings (winding overhang) of turbo-generators poses certain problems because of the high stresses to which these winding overhangs are subjected. The origin of these stresses lies in electromagnetic force effects, in particular in the case of short-circuiting, in vibration phenomena and in differences between the thermal expansion of the stator bars and that of the stator iron during operation. These loads lead sooner or later to instances of loosening and wear phenomena, which lead ultimately to earth shorts and short circuits.
A number of systems have been introduced to improve the strength of the winding overhangs of large electric machines, the majority of these systems working with one-piece rings made from insulating material as the central support element.
In the device for holding the ends of the turns of a stator winding in an electric machine according to German Offenlegungsschrift 1,613,125, an outer ring fits closely from outside against a portion of the external layers of the ends of the turns. An inner ring, which is independent of the outer ring, engages on the inner layers of the ends of the turns. In order to prevent axial displacement of the two rings relative to one another, devices in the form of C-shaped bows which embrace the ends of the turns are provided to connect the two rings. The two rings are screwed to axially extending holders which, for their part, are attached to the end of the stator laminated core.
The winding overhang holder according to U.S. Pat. No. 4,800,314 uses just one outer ring. The winding overhang ends are wedged and bonded together in groups and fastened to this outer ring by means of bands.
A further solution to the problem of support, intended particularly for retrofitting, is the subject-matter of U.S. Pat. No. 5,140,740 which is identical in content. The holder proposed there has an inner ring which fits closely against the ends of the turns of the stator winding, which ends widen like an internal taper. The external support consists of an at least two-part ring or of supporting beams which extend in the circumferential direction and are interconnected.
Tie rods which engage on the inner ring and outer ring or on the supporting beams serve to brace the inner ring and the external support. Alternatively, in the known solution, the outer ring and the tie rods can be dispensed with (FIG. 4). Together with the end bows of the winding overhang, the inner ring is then supported, with the interposition of clamping wedges, on supports which are attached to the end of the stator laminated core. The disadvantage in both alternatives is that when the winding overhang unit becomes loose, they can only be retightened with a great deal of effort.
Common to all the known embodiments is that the external support is provided by rings. Rings of this kind expand under the action of the rotating electromagnetic forces, become oval and can thus fulfill their supporting function only in part.